Interexchange switching telephone system



Aug. 28, 1951 J. wlcKs INTEREXCHANGE swITcx-IING TELEPHONE sYsTEzM 9 Sheets-Sheet l Filed Dec. 12, 1947 Aug. 28, 1951 J. WICKS' 2,566,009

INTEREXCHANGE SWITCHING TELEPHONE SYSTEM Filed Dec. 12, 1947 9 Sheets-Sheet 2 From Sw. Bd FIG. 2 N 9004 Trunk Cir.

T E U IT T 'I 9 21H one [29h \3l5 |22| 222 I Repeater Repeater lo 2IO 220 240 214Jr f- 244 242f Inc. Sel Inc; Sel. Inc. Sel. 2|2"/ 205 235 250 r: I f L:

2I3 243 *If Finder Sel. CCOVHU Finder Sel. Comb.

v202 203 A o n204 232, 233 Conn234 REMOTE EXCHANGE CENTRAL OFFICE IO 2O FIG. IO

INVENTOR. John Wicks BY Aag. 2s, 1951 J. wxcKs 2,566,009 INTEREXCHANGE swITcHING TELEPHONE SYSTEM Filed Dec. 12, 1947 9 sheets-sheet s CSW/wn C3|9^/C3H\ Repen'fer 30.0 K Tggdem 56| Ans. C3|4\ R340 TJ;

BUSy C 3Q l INVENTOR By. John W|cks Aug. 2s, 195.1. WMS 2,566,009

INTEREXCHANGE SWITCHING TELEPHONE Filed Deo. l2, 1947 9 Sheets-Sheelrl 4 Repeater 300v THRU 495 IN VEN TOR.

4 BY John V`Vicks Ahvs.

Aug. 2s, 1951` J WMS 2,566,009 INTEREXCHANGE SWITCHING TELEPHONE SYSTEM Filed Dec. 12, 1947 9 sheets-sheet 5 FIG.. 5 REPEATER 30o 'ZRR-C505 9 Mon ,cso R@ v 9 513 -TRKh 5? 6/`3L -f SEND\ -,c5o2

538 I 537VFM- I MoN. ,C504

' T RK, L-REQsos R530 I Cow/542 l ,slswAL'lNsos ,DIAL IN /c5|o 'll-0 'Ikg 52 535, START S2M/ .TIMER W2 |MPULSE= 546L--c't wTAY Y L STA ION @MTW-M552 L 553 ,osu Pulse cunj TONE UNIT PULSLE 50' -lRfl TlMER SW. 75' INVENTOR. T5570 John Wicks M574 ROT, M573 571 m BY O D C O O O 'agsc-ga 910 Ays4 Aug, 2s, 1951 J. WICKS 2,566,009

INTEREXCHANGE SWITCHING TELEPHONE SYSTEM Filed Dec. 12, 1947 I 9 Shee'cS-Shee 6 TIMER sw. Tse-lo AIIys Aug. 28, 1951 J. WICKS INTEREXCHANGE SWITCHING TREPHONE SYSTEM v Filed Dec. 12, 1947 9 Sheets-Sheet '7 SIG IN FIG. 7

INVENTOR.

John Wicks BY v AHys

Aug. 2s, 1951 J. WICKS INTEREXCHANGE SWITCHING TELEPHONE SYSTEM Aug, 28, 1951 J. wlcKs INTEREXCHANGE swITcHING TELEPHONE SYSTEM Filed Dec. 12, 1947 9 Sheets-Sheet 9 ATTyS Patented Aug. 28, 1951 INTEREXCHANGE SWITCHING TELEPHONE SYSTEM John Wicks, Biloxi, Miss., assigner to Automatic Electric Laboratorieslnc., Chicago, Ill., a corporation of Delaware Application December 12, 1947, Serial No. 791,298

13 Claims.

1 The present invention relates to automatic telephone systems, and more particularly to such lsystems of the interexchange switching type.

In automatic telephone systems, recently it has become feasible to permit subscribers at substations in the different exchanges of the system to set up telephone connections utilizing automatic switching apparatus and involving eX- changes disposed considerable distances apart; which connections have always heretofore been completed by operators at switchboards in central oiiices and otherwise handled strictly on a toll basis. This situation presents a number of operating problems since a substantial number of the existing trunk lines interconnecting remotely disposed exchanges are of such length that they incorporate ampliers of the vacuum tube type embodying automatic volume control features; which amplifiers are ordinarily so constructed and arranged that they will pass only audio frequency signals. Consequently, it is impossible to employ, in conjunction with these trunk lines, ordinary dialing schemes for the purpose of controlling the automatic switching apparatus.

This general problem has been encountered heretofore in toll switching telephone systems as disclosed in U. S. Patent No. 2,155,176, granted on April 18, 1939, to John Wicks, wherein a toll switching telephone system is provided that comprises audio frequency carrier repeaters governed by operators at switchboards in central o'ices. Also an improved toll switching telephone system of this type is disclosed in the copending application of John Wicks and Otho D. Grandstaff, Serial No. 749,758, filed May 22, 1947, now Patent No. 2,517,516, granted August l, 1950, the lastmentioned system incorporating an improved tone unit disclosed in the copending application of I@tho D. Grandstaff, Serial No. 738,194, filed March 29, 1947, now Patent No. 2,482,478, granted September 20, 1949.

While the repeaters of these toll switching telephone systems are capable of controlling automatic switching appartus over long toll lines incorporating amplifiers of the type noted, these repeaters are so constructed Iand arranged that they, in turn, must be governed by operators at switchboards in central oices.

Accordingly, it is a general object of the present invention to provide an automatic telephone system wherein subscribers at substations in the different exchanges of the system may set up connections utilizing automatic switching apparatus and involving exchanges disposed considerable distances apart.

(CIL 179-18) Another object of the invention is to provide an automatic telephone system of the type noted, comprising exchanges interconnected by trunk lines incorporating amplifiers of the vacuum tube type Capable of passing only audio frequency signals.

Another object of the invention is to provide an audio frequency carrier repeater that is so constructed and arranged that it may be governed from -a subscriber substation.

Another object of the invention is to provide an audio frequency carrier repeater that is so constructed and arranged that it is capable of returning supervisory signals in such form that they may be received and comprehended at a subscriber substation.

A further object of the invention is to provide an audio frequency carrier repeater of improved circuit connection and arrangement.

A still further object of the invention is to provide in an automatic telephone system of the type noted, which also comprises a switchboard and one or more way stations, an improved arrangement for setting up connections between the switchboard and the way station via a trunk line, without interference with the setting up of connections between the subscriber substations in two remotely disposed exchanges over the trunk line.

Further features of the invention pertain to the particular `arrangement of the circuit elements of the system, whereby the above-outlined and additional operating features thereof are attained.

Sect. 1.-The general arrangement of the telephone system The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings in which Figure 1 is a schematic diagram of the area served by a telephone system embodying the present invention and illustrating the general arrangement of the apparatus incorporated in several of the exchanges and the oilice thereof; and Figs. 2 to 9, inclusive, taken together, illustrate the details of certain of the apparatus incorporated in the central office and in the distant exchange of the telephone system, which apparatus has embodied therein, the feature of the invention as briefly outlined above. {Specifically, in order to form a unified diagram, Figs. 2 to 8, inclusive, should be arranged vertically in side-by-side relation from left to right, and Fig.

9 should be arranged horizontally above Fig. 4 and partially above Fig. 5, as illustrated in Fig. l0.

More particularly, Figs. 3 to 5, inclusive, illustrate the details of one of the repeater circuits incorporated in the central oiiice; Figs. 6 to 8, inclusive, illustrate the details of one of the repeater circuits incorporated in the distant exchange; and Fig. 9 illustrates the details of one of the cord circuits and of one of the trunk circuits disposed the switchboard in the central oiice.

Referring now more particularly to Fig. l, the telephone system there illustrated serves an area comprising a remote exchange lil, a central olce 2G, and a distant exchange 3Q. The remote exchange i6 is of the automatic type, serving a number or subscriber substations, including the subscriber substation T3, and comprising automatic switching apparatus. Similarly, the central ofce 20 is of the automatic type, serving a number of subscriber substations, including the subscriber substation T2, and comprising automatic switching apparatus. Likewise, the distant exchange 3o is of the automatic type, serving a number of subscriber substations, including the subscriber substation Ti, and comprising automatic switching apparatus. The switching apparatus provided in the remote exchange il! ccmprises a number of groups of Ender-selector links, the nrst group including the link constituting the finder 232 and the selector 2&3; as well as a number of groups of combination toll and local connectors, the rst group including the combination connector 2cd. The finder 292 has access to the iirst group of subscriber lines, including the subscriber line 2b! extending to the subscriber substation T3; and the combination connector 2SA is accessible to the selector E via a trunk 2|3 and, in turn, has access to the first group of subscriber lines mentioned. Similarly, the switching apparatus provided in the central oiice 20 comprises a number of groups of finder-selector links, the first group including the link consisting of the finder 232 and the selector 233; as Well as a number of groups of combination toll and local connectors, the rst group including the combination connector 23s. The nder 232 has access to the iirst group of subscriber lines, including the subscriber line 23| extending to the subscriber substation T2; and the combination connector 234 is accessible to the selector 23 via a trunk 243 and, in turn, has access to the rst group of subscriber lines mentioned. Like- Wise, the switching apparatus provided in the distant exchange til comprises a number of groups of finder-selector links, the first group including the link consisting of the finder SEZ and the selector 893 as Well as a number of groups of combination toll and local connectors, the nrst group including the combination connector tre. The nder BSZ has access to the nrst group of subscriber lines, including the subscriber line 8i?! extending to the subscriber substation TI; and the combination connector 8st is accessible to the selector 833 vial a trunk 8&5 and, in turn, has access to the rst group of subscriber lines mentioned.

Also the remote exchange lil comprises groups of local connectors, not shownl having access to the different groups of subscriber lines, the nrst group having access to the first group of subscriber lines, including the subscriber line 26| extending to the subscriber substation T3. Similarly, the central office 29 comprises groups of local connectors, not shovvny having access to the different groups of subscriber lines, the rst group having access to the rst group of subscriber lines, including the subscriber line 215i extending to the subscriber substation T2. Likewise, the distant exchange 39 comprises groups of local connectors, not shown, having access to the diiferent groups of subscriber lines, the first group having access to the irst group of subscriber lines, including the subscriber line extending to the subscriber substation Tl.

The remote exchange ID and the central office 2D are interconnected by a plurality of trunk lines, including the trunk line 220, each incorporating a plurality of voice current repeaters and terminating in repeaters respectively disposed in the remote exchange I@ and in the central office 26. For example, the trunk line 223 incorporates a number of voice current repeaters, including the voice current repeaters 224 and 222, and terminatos in the repeaters 2HE and 213i) respectively disposed in the remote exchange l@ and in the central oflce 2t. Each repeater in the remote exchange i0 is provided with a tone unit individual thereto, is accessible via an incoming,` trunk thereto, and has access via an outgoing? A`trunk therefrom to an individually associated in-I coming selector. For example, the repeater 2id' is provided with a tone unit 2l i individual thereto, is accessible via the incoming trunk 2I2 thereto, and has access via the outgoing trunk 2M therefrom to the individually associated incoming selector 295. The incoming trunk 2&2 is accessible to the selectors 233, etc., of the associated links; While the incoming selector 2% has access to the different groups of combination connectors 204, etc. Each repeater in the central olce 2li is provided with a tone unit individual thereto, is accessible via an incoming trunk thereto, and has access via an outgoing trunk therefrom to an individually associated incoming selector. For example, the repeater 24E is provided With a tone unit 2M individual thereto, is accessible via the incoming trunk 242 thereto, and has access via the outgoing trunk 2li@ therefrom to the individually associated incoming selector 235. The incoming trunk 242 is accessible to the selectors 233, etc., of the associated links; While the incoming selector 2?:5 has access to the diferent groups of combination connectors 236, etc.

The central ofce 2li and the distant exchange Se are interconnected by a plurality of trunk lines, including the trunk line 5|5, each incorporating a plurality of voice current repeaters and terminating in repeaters respectively disposed in the central oflice 20 and in the distant exchange 3D. For example, the trunk line 515 incorporates a number of voice current repeaters, including the voice current repeaters 53 and M3, and terminates in the repeaters 33B and 80d respectively disposed in the central office 2l] and in the distant exchange 323. Each repeater in the central oflice 2t is provided with a tone unit individual thereto, is accessible via an incoming trunk thereto, and has access via an outgoing trunk therefrom to an individually associated incoming selector. For example, the repeater 30D is provided with a tone unit 59.4 individual thereto, is accessible via the incoming trunk 3 I il thereto, and has access via the outgoing trunk 315 therefrom tothe individually associated incoming selector 25e. The incoming trunk. 3H) is accessible to the selectors 233, etc., of the associated links;.vvhile the incoming selector 259 has access to the different groups of combination connectors 234, etc. Each repeater in the distant exchange 35 is provided with a tone unit individual thereto, is accessible via an in- `sub'stations "T2, etc., type and are provided with conventional equipi.

ascenso,

coming trunk thereto, vand has access via anoutgoing trunk therefrom to an individually vassociated incomingv selector. For example, the trepeater 600 is provided with a tone unit 50i individual thereto, is accessible via the incoming trunk SIU thereto, and has access via theoutgoing trunk 815 therefrom to the individually associated incoming selector 805. The incoming trunk 8|0 is accessible to the selectors 803, etc., of the associated links; while the incoming .selector 805 Vhas* access to the dierent groups of combination connectors 804, etc.

Also, a plurality of way stations are disposed between the central'oilice 20 and the distant exchange 30 and are connected to one of the trunk lines extending therebetween; the way stations Wl and W2 'being illustrated as connected to the trunk line 515 intermediate the voice current repeaters 5l Sand BIS incorporated therein. Further, the central oice 20 comprises `a manual switchboard 500 having access to trunk circuits individually associated with the repeaters in the central ofiice 2.0. More particularly, the repeater 24E terminating the trunk line 220 extending between the remote exchange I0 and the central cfce 20 is provided with a trunk circuit 265 individual thereto that is connected to the incoming trunk .242. Similarly, the repeater 300 terminating. the trunk line 515 extending between the cen- :tral o'ice 2lil and the distant exchange 30 is provided with a trunk circuit 920 individual thereto that is connected both to the incoming trunk 3m and'to `the trunk line 515.

Finally, in the central oice 20, it is noted that the incoming selector 235 individual to the re- `peater 240 also has access to the incoming trunk 315. extending to the repeater 300; while the incomingselector 250 individual to the repeater 300 also has access to the incoming trunk 242 extending to the repeater 240; whereby calls originating in the remote exchange I0 maybe extended through the central oice 20 to the distant exchange 30, and calls originating in the distant exchange 30 may be extended through the -central oiiice 20 to the remote exchange I0.

Sect. 2.-The yarmaratus incorporated in the telephone' system In the remote exchange l0, `the automatic switching apparatus, including the iinders 202,

ete., the selectors 263, etc., the local connectors, not shown, the combination connectors 204, etc., the incoming selectors 205, etc., are ci the welllknown Strowger types; the groups ci nder-selector links are provided with conventional disl 'the incoming selectors 235, 250, etc., lare of the well-known Strowger types; the groups of nderselector links are provided with conventional distrihuting apparatus, not shown; Ithe subscriber are of the common battery ment; Vand the subscriber lines 231, etc., are provided with conventional line circuits, not shown. Likewise, in the distant exchange 30, the automatic switching apparatus,.including the finders 852, etc., the selectors 803, etc., the local connectors,..nct shown, 'the combination zconnectors=-804, etc., fthe' incoming selectors 805, retc., areof thel well-.linown Strowger` types; the groupsY `of finder-selector links are Vprovided with conventionalY .distributing apparatus, not shown; the subscriber substations 'I'.I ,fetc. are oi-:the common battery type and are provided with' :conventional equipment; and :the subscriber ylines f8 iii etc., are provided with conventional line circuits, not shown.

The repeaters 2 l 0, etc., in the Vremote yexchange ifi, the repeaters ..240, 30.0, etc, in the Vcentral ciice 20 and the repeaters 600, etc'., inthe distant exchange 30 4are'identical. The-*repeater lillfin theA central cnice' 20 is illustrated in details in Figs. -3 .to 5inclusivelas comprising a relay group including. twov :release .pulse 'timer relays R315V and R325-, a control relay R325, .a Atime pulse ree lay R330; a tandem test relay R340', an out-seize relay,2R350,1a;sequence relay R350', an answer relay R350; an answer supervisory .relay R315, a loci: relay R330, aline relay R390', a dial-in relay R'all', astart pulse relay R520, a reverse battery rel'ayRiU, an 'in-seize relay R540, fa Arelease relay Rliikvra signal-'in relay 'R0-60, a control relay R515', arswitc'h-through relay R485, a pulse? relay RSil, apreparerelay R495, ahold'relaylRw, two pulse relays Rland R525, a control rela-y R530',A an impulse Arelay R535, a control relay `aftimer relay R545, a timer startrelay lSt550,.and Ltwo timer relays R550 and 1:"555,y .Also the repeater 3300 comprises` a repeating coil ROMS', a busy lamp 143252- and a timer switch T5550 of the -minor type. The timer s-w-itch *ESMQS comprises two wipers 51| and 5!'2V provided with -an :associated rotary ycontact bank, a rotary magnet M513 vfor -fdriving theV wipersnotedf 'step byv step away' from their home positionsv acrossithe associated contact bank, and a release magnet M51'I4fifor releasing the wipers noted andfor returning them -to their h'omeipositionsl Also, aset of switch springs S515 is associated with the wipers`v noted, that-isiactuated when they Yare-tnoved away from-their home positions'.

Similarly, the repeater e' inthe-:distant exchange 305s :illustrated in y'detail in Figs'. 6-to -8, inclusive, asucom-prising a relayg-roup including two release pulse timer relays R565? andi-RBZDQ- a control A:relay R825, a vtime pulse relay R530?, a tandem test relay R840, an out-seize Vrelay R058, afsequence'relay R860; `an answer relayRSrT, an answer supervisory relay R3115- a lock relay R880', Ia line relayiiRelJ, a dial-in relay Rilima' start pulsefrelayR'lZ-U, a .reversebattery relay R'lllisan -in-seize relay R'i40,.a release relaysR'lEl, :a signalinwrelay- R'l'ngxa control. relay ZRHB; a Lswitchthrough relay R185, a pulse .relay R; av :prepare relay' R195-, alhold relay R100, two pulse `relays 'RE20fand'R525g a-control relay R530, .an impulse {rela-31.115.535, Va control relay` R640, a timer relay R545', a-timer start relay R550, and two timer .relays R560' andv R655. Also lthe repeater '55.0 comprises a repeating coil RC'I00, av Ibusy lamp -la22and a timer switch Ts'lilof th'eminor type. r-I2hetimer vswitch T5510" comprises two wipers :Eiland =61-2 provided with an associated rotary `contactbaille a rotary magnet M513 'for driving the wipersnotedstep .by stepA away from their home `positions acrossl the associated Contact fbanlf., and -a release magnet M511! yfor releasing the wipers'notedzandior returning themto -their home positions, Also aset of switch springs S575 isassociated with the wipers ynotedthat 4isact ra.ted.when theyare moved away from 4their home positions.

The voice current repeaters 221, 222, etc., incorporated in the trunk lines 220, etc., extending between the remote exchange and the central office 20, as well as the voice current repeaters 513, 613, etc., incorporated in the trunk lines 515, etc., extending between the central oice and the distant exchange 30, are of the conventional vacuum tube automatic gain control type. The way stations W1 and W2 connected to the trunk 515 extending between the central oice 20 and the distant exchange are of the local battery type and are provided with conventional magneto type telephone equipment.

The trunk circuits 245, etc., respectively individually associated with the repeaters 240, etc., terminating the trunk lines 220, etc., extending between the remote exchange 10 and the central ot'ce 20 are identical and of 'any suitable type; while the trunk circuits 920, etc., respectively individually associated with the repeaters 300, etc., terminating the trunk lines 515, etc., extending between the central ofce 20 and the distant exchange 30 are identical. Specifically, the trunk circuit 920 individually associated with the repeater 300 is illustrated in Fig. 9 and comprises a relay group including two sleeve relays R930 and R940 and a cut-off relay R950. Also the trunk circuit 920 comprises a drop D902, a busy lamp L911, a regular trunk jack J 910 and a way station jack J 903. The regular trunk jack J 910 is utilized by the operator at the switchboard 900 to seize the repeater 300 when a call is to be extended to a subscriber substation in the distant exchange 30; While the way station jack J 903 is utilized by the operator at the switchboard 900 to seize the repeater 300 when a call is to be extended to one of the way stations W1 or W2 or when a call is to be answered from one of the way stations W1 or W2. Thus the regular trunk jack J910 is a one-way outgoing jack; while the Way station jack .1903 is a two-way outgoing and incoming jack.

In passing, it is noted that each of the trunk circuits 245, etc., associated with the repeaters 240, etc., comprises a regular trunk jack, not shown, accessible to the operator at the switchboard 900, which is utilized to seize the associated repeater 240, etc., when a call is to be extended to a subscriber substation in the remote exchange 10.

Finally, the switchboard 900 comprises a plurality of cord circuits; a fragmentary portion of the cord circuit 960 being illustrated in Fig. 9 as comprising a plug P961, a talk key K961, a dial key K962 and a ring key K963, as well as a headset 963 and an impulse transmitting mechanism in the form of a dial 964.

The tone units 211, etc., in the remote exchange 10, the tone units 241, 501, etc., in the central office 20, and the tone units 601, etc., in the distant exchange 30 are identical; each being of the type disclosed in the co-pending application of Otho D. Grandstaff, Serial No. 738,194 filed March 29, 1947. For example, the tone unit indicated in Fig. 5 comprises both a sender and a, receiver of unmodulated audio frequency signals and fixed frequency modulated audio frequency carrier signals. Specifically, the tone unit 501 is adapted to send and toV receive unmodulated 1000 cycle audio frequency signals as well as to send and to receive 60 cycle modulated 1000 cycle audio frequency carrier signals; which signals are utilized for the purpose of digit control, seizure control, supervisory control and release control as explained more fully hereinafter. Also the tone unit 501 comprises a modulation cut-off relay, a receive switch relay, a pulse cut-in relay, an impulse-in relay and a signal-in relay; as well as a group of conductors extending to the associated repeater 300 and including a sending -conductor C501, a, sending -i-conductor C502, a monitoring conductor C503, a monitoring -l-conductor C504, a receiving conductor C505, a receiving +conductor C506, a receiving switch conductor C501, a modulation cut-off conductor C508, a signal-in conductor C509, a dial-in conductor C510, and a pulse cut-in conductor C51 1. Finally, the tone unit 501 comprises a 60 cycle generator and a 1000 cycle generator as well as a vacuum tube relay circuit.

A better understanding of the connection and arrangement of the apparatus incorporated in the telephone system will be facilitated from a consideration of the extension of calls involving the various subscriber substations in the remote exchange 10, the central office 20 and the distant exchange 30, as well as the extension of calls involving the switchboard in the central ofce and the way stations, appearing hereinafter.

Sect. 3.-Local calls ln the remote exchange 10 a call may be extended from a calling subscriber substation in the iirst group, such for example, as the callingr subscriber substation T3, via the subscriber line 20|, the finder 202, the selector 2113 and a local connector in the first group, not shown, to a called subscriber substation in the first group. Also in the event all of the local connectors in the first group, not shown, are busy, the call may lbe routed via the trunk 213 to the combination connector 204 in the rst group and thence completed to the called subscriber substation in the first group. Similarly, in the central oflice 20, a call may be extended from a calling subscriber substation in the first group, such, for example as the calling subscriber substation T2, via the subscriber line 231, the finder 232, the selector 233, and a local connector in the first group, not shown, to a called subscriber substation in the first group. Also in the event all of the local connectors in the first group, not shown, are busy, the call may be routed via the trunk 243 to the combination connector 234 in the first group and thence completed to the called subscriber substation in the first group. Likewise, in the distant exchange 30, a call may be extended from a calling subscriber substation in the iirst group, such, for example, as the calling subscriber substation T1, Via, the subscriber line 801, the finder 802, the selector 803 and a local connector in the rst group, not shown, to a called subscriber substation in the first group. Also in the event all of the local connectors in the first group, not shown, are busy, the call may b'e routed via the trunk 806 to the combination connector 604 in the first group and thence completed to the called subscriber substation in the first group. These operations are entirely conventional and are not described in detail in the interest of brevity.

Sect. 4 A call from a subscriber substation in the central ofice to a subscriber substation in the distant exchange.

Now assuming that a call has been initiated at the calling subscriber substation T2 in the central office 20, that the finder 232 of the link illustrated has operated to seize the subscriber line 231 extending to the calling subscriber substation T2 and that the selector 233 of the link `is-conditioned to respond to the rst digit dialed, the subscriber at the calling subscriber substation T2 proceeds to dial a predetermined -prefix digit; whereby the selector 233 is operated to select the group of trunks, including the trunk 3|0, and then an idle trunk in the selected group. For example, the selector 233 may select the particular trunk 3H!k extending to the repeater 300, the trunk 3|0 being marked as idle by the application of battery potential upon the control conductor C3|3 thereof Via `the contacts 454, 444', 561, 308 and the lower -windingof the out-seize relay R350. When the selector 233 seizes the trunk 3|-0, ground potential therein is applied to the control conductor C3| 3 of the trunk 3|0 in order to complete a circuit substantially identical to thatftraced above for energizing the lower winding of the out-seize rellay R350 causing the latter relay to operate. Also Ya loop circuit is completed between the callin'gsubscriber substation T2 and the upper and lower windings of the line relay R390 inthe repea-ter 300; whereby the latter relay operates. Theloop circuit mentioned extends from ground potential by way of the lower winding of the line relay R390, the contacts 434 and 446 and the winding W402 of the repeating coil `RC400 to the line conductor C3l2; and from battery potential by way of the upper winding of the line 'relay R390, the contacts 432 and `441i and the vwinding W453i of the repeating coil RCiie 'to the line conductor C3||; the line conductors A(33H and C3|2 of the trunk 3|0 being connected together, Via the selector 233, the iindcr 232 and 'the line conductors of the subscriber line 23|, at the calling subscriber substation T2.

Upon operating the out-seize relay R350 completes, at the contacts 355, a path, including the contacts 561 and 368, for short-circuiting the upper winding thereof; and completes, at the contacts 354, a circuit, including the contacts 1140 and the resistor 393, for operating the lock relay R380. Upon operating the line relay R390 completes, at the contacts 392, a circuit, including the contacts 405, for operating the start pulse relay R420; and completes, at the contacts 39|, a point in multiple to the contacts 384', for applying ground potential via the contacts 405 to the receiving switch conductor C50-1 extending to the tone unit 50|. Upon op- `erating the lock relay R380 interrupts, at the contacts 384.', one of the multiple paths for applying ground potential to the receiving switch conductor C501; and completes, at the contacts 138|', a circuit, including the contacts 365, 461 iand 56|, for operating the timer relay R545. 'Also the lock relay R380 completes, at the contacts, 333, a path for applying ground potential -to the hold conductor 030|; thereby to complete a path, including the contacts 33| and the con- Vlductor C302, for illuminating the busy lamps A11322 and L9|| and a direct circuit for operating the cut-on relay R950. The illumination of the busy'lamp L322, indicates the busy condition of the repeater 300; and the illumination of the busy lamp L9I| associated with the regu- Alar trunk jack J 9|0 at the switchboard 900 indicates the busy condition of the terminated Vtrunlr3|0 extending to the repeater 300 to the `operator thereat. Upon operating the cut-01T relay R050 interrupts, at the contacts 95| and i052, the path, including the condenser 90|, for fbridging the drop D902 at the switchboard 900 across the line conductors of the trunk line-'SI5 10 in order to prevent operation of the drop D002 atv this time. Also the application of ground potential to the hold conductor C30| completes a circuit for energizing the left-hand winding of the answer relay R310; whereby the latter relay is conditioned to operate when the righthand winding thereof is subsequently energized and properly poled.

Upon operating the start pulse relay R020 completes, at the contacts`422, a circuit for op erating the hold relay R000; and completes, at the contacts l3.25, a holding circuit, including the contacts 392 and the resistor .4|5, for energizing the winding thereof. Upon operating the timer relay R545 completes, at the contacts 543, a circuit for energizing the winding of the timer relay R535 in order to cause the latter relay to operate shortly thereafter, it being of theslowtc-operate type. Also the timer relay R505 completes, at the contacts a holding circuit, .including the contacts 431 and 53|, for energizing the winding thereof; completes, at the contacts 501, a circuit, vincluding the contacts .552, for energizing the upper winding of the prepare relay R495 in order to cause the latter relay to operate, and completes, at the contacts 541, a multiple circuit, including the contacts 552, 388, 381 and 065, for operating the control relay R510; and completes, at the contacts 541 and 545, a circuit, including the contacts 552, for energizing the upper winding of the pulse relay R520 in order to cause the latter relayto operate. Upon operating the prepare relay R495 interrupts, at the contacts 436', the path for applyingground potential to the receiving switch conductor C501. Upon operating the holdrelay R400 completes, at the contacts 402, a holding circuit, including the contacts 495' and 39.1, for

energizing the winding thereof; completes, at

,f the contacts 403, a path, including the contacts 356, 444and 454, for applying ground potential to the control conductor C3113 of the trunk 3|0; and completes, at the contacts 003, a multiple holding circuit, including the contacts 356, y531, and 368, for energizing the lower winding of the out-seize relay R350. Also the hold relay R400 interrupts, at the contacts 505, the original operating circuit for .the start pulse relay R020;

and completes, at the contacts 404, a priming circuit, including thecontacts 402, the resistor 4|9 and the adjustable resistor 4|8, for energizing'the winding of the pulse relay R490; and completes, at the contacts 404, a priming circuit, including the contacts 423 and the resistor 4| 6, for energizing the winding of the puls-e relay R525. Further, the hold relay Rlilcornpletes,

at the contacts 40|, a priming circuit, including the contacts 499 and the resistor 524, for energizing the upper winding of the pulse relay R520.

Upon operating the control relay R410 interrupts, at the contacts 01| and 413, the normal connection including the contacts 08| and 433, between the monitoring conductor C503 and the monitoring -l-conductor C505 and the windings W403 and W404 of the repeating coil RC500; and completes, at the contacts 12, a pathfor short-circuiting the winding W501i of the repeating coil 12.0400. Also the control relay R310 completes, at the contacts 310, a path for shortcircuiting the right-hand winding of the answer relay R310; and completes, at the contacts 415, a holding circuit, including the contacts 490, for energizing the lower winding of the prepare vrelay'R405. Upon operating the pulse relay vR520 ll completes, at the contacts 52|, a circuit, including the resistor 525, for operating the impulse relay R535; and completes, at the contacts 522, a circuit, including the contacts 494, the resistor 4|6 and the contacts 423 and 404, for operating the pulse relay R490. Upon operating the impulse relay R535 interrupts, at the contacts 536, a normally completed path for shorting together the sending conductor C55! and the sending -i-conductor C502; whereby the sending conductor C50I is effectively connected Via the contacts 491 to the negative line conductor of the trunk line 5l5 and the sending -i-conductor C502 is effectively connected via the condenser 531 and the resistor 533 to the positive line conductor of the trunk line 515. When the timer relay R565 operates, it completes, at the contacts 566, a circuit for energizing the winding of the timer relay R560 in order to cause the latter relay to operate shortly thereafter, it being of the combination slow-to-operate and slow-to-release type. Also the timer relay R565 interrupts, at the contacts 561, the path for short-circuiting the upper winding of the outseize relay R350; whereby the upper and lower windings of the out-seize relay R350 are energized in series circuit relation via a holding circuit, including the contacts 403 of the operated hold relay R400` Further the timer relay R565 completes, at the contacts 565, a circuit, including the contacts 363, for energizing the lower winding of the sequence relay R360; whereby the latter relay operates through its first step completing, at the contacts 352, a path, also including the grounded hold conductor C36! for shortcircuiting the upper winding thereof; whereby further operation of the sequence relay R350 is prevented at this time. When the timer relay R560 operates, it completes, at the contacts 562, a circuit for operating the control relay R540; and interrupts, at the contacts 561, the circuit for energizing the winding of the timer relay R545 in order to cause the latter relay to restore shortly thereafter, it being of the slow-to-release type. Uon operating the control relay R540 completes, at the contacts 542, a circuit for operating the control relay R530. When the timer relay R545 restores, it interrupts, at the contacts 548, the circuit for maintaining operated the timer relay R565; and interrupts, at the contacts 546 and 541, the circuit for energizing the upper winding of the pulse relay R520 in order to cause the latter relay to restore shortly thereafter, it being rendered slightly sloW-to-release by virtue of the completed path, including the adjustable resistor 523, for short-circuiting the lower winding thereof. Also the timer relay R545 interrupts, at the contacts 541, the original operating circuit for energizing the upper winding of the prepare relay R495 and the multiple circuit for energizing the winding of the control relay R410 in order to cause the latter relay to restore shortly thereafter, it being of the slow-to-release type. Upon restoring the pulse relay R520 interrupts, at the contacts 521, the circuit for maintaining operated the impulse relay R535. Upon restoring the impulse relay R535 again completes, at the contacts 536, the shorting connection between the sending -conductor C50! and the sending -i-conductor C502 whereby the sending conductor C501 and the sending +con ductor C502 are effectively disconnected from the negative and the positive line conductors of the trunk 5l5. Upon restoring the timer relay R565 interrupts, at the contacts 566, the circuit for energizing the winding of the timer relay R560 in order to cause the latter relay to restore shortly thereafter, it being of the combination slow-to-operate and slow-to-release type. Also the timer relay R565 interrupts, at the contacts 566, the previously traced circuit for energizing the lower winding of the sequence relay R360 and the previously traced path for short-circuiting the upper winding thereof; whereby the sequence relay R360 operates through'its second step. Also the timer relay R565 again completes, at the contacts 561, the path for short-circuiting the upper winding of the out-seize relay R350; whereby the holding circuit for energizing the lower winding of the out-seize relay R350 is recompleted.

|lhe sequence relay R360 operates through its second step by virtue of the completed circuit for energizing in series the upper and lower windings thereof; and interrupts, at the contacts 363, the connection to the junction between the upper and lower windings thereof. Also the sequence relay R360 completes, at the contacts 36|, a path for applying ground potential through the lower winding of the tandem test relay R340 to the EC conductor C314 of the trunk 310 extending back to the selector 233; whereby a test is made by the tandem test relay R340 in order to determine whether the incoming circuit includes another repeater; which circumstance does not exist in the present example since the present call originates at the calling subscriber substation T2 in the central office 20. Accordingly, the tandem test relay R340 is not operated in the present example. Also the sequence relay R360 completes, at the contacts 366, a connection including the contacts 382 and 336, between the timer conductor C394 and the junction between the upper and lower windings of the time pulse relay R330. At this point it is noted that ground potential is applied to the timer conductors C394 and C395 intermittently, ground potential being retained upon the timer conductor C394 when applied thereto throughout a time interval of approximately one minute and ground potential being retained upon the timer conductor C395 when applied thereto throughout a timer interval of approximately ve minutes; which arrangement is utilized in conjunction with the time pulse relay R330 for a purpose more fully explained hereinafter. Further the sequence relay R360 completes, at the contacts 363, a path, including the contacts 351 and 489, for applying battery potential by way of the resistor 358 to the modulation cut-off conductor C508; and completes, at the contacts 364, a holding circuit, including the contacts 38| and the resistor 393 for energizing the winding of the lock relay R380. Upon restoring the control relay R410 interrupts, at the contacts 412, the path for short-circuiting the winding W403 of the repeating coil RC400; recompletes, at the contacts 41! and 413, the normal connection between the windings W403 and W404 of the repeating coil RC400 and the monitering conductor C503 and the monitoring -l-conductor C504. Further the control relay R410 interrupts, at the contacts 414, the path for short-circuiting the right-hand winding of the answer relay R310; and interrupts, at the contacts 415, the holding circuit for energizing the lower winding of the prepare relay R495 in order to cause the latter relay to restore. Upon restoring the prepare relay R495 recompletes, at the contacts 499, the priming circuit, including the contacts 40| and the resistor 524, for energizing the upper winding of thevpulse relay R520; interrupts, at the contacts 405', the holding vcir'- cuit for energizing the winding of the hold relay R400; and recompletcsat the contacts 495', the path for applying ground potential tothe receiving switch conductor C501. Upon restoring the timer relay R500 interrupts, at the contacts 562, the circuit for energizing the winding of the control relay-R540, thereby to cause the latter relay to restore shortly thereafter, it being of the slowto-release type. Upon restoring-the control relay R550 interrupts, at the contacts 542, the circuit for energizing the winding of the control relay R530 in order to cause the latter'relay to 'restore shortly thereafter, it lbeing of the slow-to-release type.

Considering new the operation of the tone unit 50| `in conjunction with the repeater 300, when the prepa-re relay R495 operated to interrupt the application of ground potential to the receiving switch conductor C501, the'receiving switch relay in the tone unit 50| restored; 'whereby the tone unit'50l was converted'from a receiving condition to a sending condition. More particularly, the tone unit 50| was rendered voperative to transmit 60 cycle modulated 1000 cycle current over the sending conductor C50| and the sending -l-conductor C502. Accordingly, when the impulse rela-y R535 operated, this 60 cycle modulated 1000 cycle current was transmitted over the negative and positive line conductors of the trunk line 515. Subsequently, when the impulse rela-y R535 restored, the sending conductor C50! and the sending -l-conductor C502 were snorted together, thereby terminating the transmission of the60 cycle' modulated 1000 cycle current over the positive and negative line conductors vof Ythe trunk. line 515. Later when the prepare relay R555 restored, ground potential was again returned upon the receiving switch conductor C501; whereby the receiving switch relay in the tone unit 50| reoperated in order again to convert the tone unit 50| from the sending condition again to the receiving condition. Accordingly, it will be understod that when the selector 233 operated to seize the trunk 3|0 eX- tending to the repeater 300 that the relays above described in the repeater 300 were operated through a cycle in order to cause the tone unit 50i to send a short .splash of 60 cycle modulated 1000 cycle current over the trunk line 5| 5 and constituting a seizure signal. Also at the conclusion of the sending of the splash of 60 cycle modulated 1000 cycle current, over the trunk line 515, the sequence relay operated to apply resistance battery potential to the modulation cut-off conductor C500; whereby the modulation cut-ofi' relay'in the tone unit 50| was operated to cut on the 60 cycle modulation Accordingly, at this time the tone unit 50| is conditioned to send unmodulated 1000 cycle current over the trunk line 5i5 under the control of the repeater 300 when ground potential is again removed from the receiving switch conductor C501 as eX- plained more fully hereinafter.

Considering-now theoperation of the tone unit in conjunction with the repeater 500, the seizure signal sent from the tone unit 50| by the repeater 300 over the trunk line |5 is repeated by the voice frequency repeaters 5|@ and 13 included therein and passes via the receiving -conductor C005 and the receiving -l-conductor C5505 into the tone unit 60|; whereby the tone unit 50i normally being in its receiving condition, responds thereto in order tol bring-about operation of the signal-in relay in the tone unit 60|; whereupon ground potential is applied during the reception of the seizure signal to the signal-in conductor C009. The application of ground potential to the signal-in conductor C009 completes a circuit for energizing the winding of the signal-in relay R in the repeater 600; whereby the latter relay operates and remains operated during the reception of the seizure signal and a short time thereafter since it is of the slow-to-release type. Uponv operating the signal-in relay R interrupts, at the contacts 162, the normal connection between the winding of the dial-in relay R1|0 and the dial conductor C0|0 extending to the tone unit 50|; and completes, atL the contacts 163, a circuit, including the contacts 884, 844 and 149, for operating the in-seize relay R140. Upon operating the n-seize relay R140 completes, at the contacts 141, a path for applying ground potential to the hold conductor C301; completes, at the contacts 148, a holding circuit, including the contacts 152 and the grounded hold conductor C80|, for energizing the winding thereof; and interrupts, at the contacts 149, the original operating circuit for energizing the winding thereof. Also the signal-in relay R completes, at the contacts 153, a multiple circuit,

including the contacts 180, for operating the switch-through relay R; and completes, at the contacts 153, a multiple circuit, including the contacts 804 and 044 for energizing the upper winding of the start timer relay R050 in order to cause the latter relay vto operate.

Also upon operating the in-seize relay R140 completes, at the contacts 14|, a path for ap'- plying ground potential to the control conductor C818- of the trunk 815 extending to the incoming selector y505; completes, at the contacts 142 and 143, connections between the line conductors C8|5 and C0|1 of the trunk SI5 and the windings `W110i and W102 of the repeating coil 11.0100; interrupts, at the contacts 144 and 140, the normal connection between the upper and lower windings of the line relay R390 and the windings W10l and W102 of the repeating coil 11C-100; and completes, at the contacts 145, a loop circuit, including'the left-hand winding of the answer relay R810. The loop circuit mentioned extends from the line conductor C8|5 of the trunk 8|5 by way of the contacts 1H and 142, the winding W10| of the repeating coil RC100, the contacts 145, the left-hand winding ofthe answer relay R810, the winding W102 of the repeating coil HC100 and the contacts 140 to the line conductor C3|1 of the trunk SI5. When the loop circuit is thus completed, the incoming selector 805 is seized and conditioned to be re#- sponsive to a digit repeated over the trunk 8|5; and the left-hand winding af the answer relay R810 is energized but is not poled to operate.

The application of ground potential to the hold conductor C80| completes a circuit for energizing the right-hand winding of the answer relay R810; and completes a multiple circuit, including the contacts 83|, for illuminating the busy lamp 1.822 in order to indicate the busy condition of the repeater 600 at this time. Further the application of ground potential to the hold conductor C80| completes a multiple circuit, includ-- ing the lcontacts 842 and Y154 vfor Aoperati-ng the control relay R110. Further the in-seize relay 'R140 completes, at the contacts 143', a path, in-

cluding the contacts 154, for applying ground potential to the control"conductor"C8'|3 of the trunk 8|0, thereby to mark the trunk 8|0 and consequently the repeater 600 as busy to the selectors 803, etc., having access thereto. Upon operating the switch-through relay R166 interrupts, at the contacts 18| and 163, the normal connections between the monitoring conductor C603 and the monitoring -i-conductor C606 extending to the tone unit 60| and the windings W103 and W`|04 of the repeating coil HC100; completes, at the contacts 182 and 184, connections, including the contacts 11|, 113 and 196, between the negative and positive line conductors of the trunk line 555 and the windings W103 and W164 of the repeating coil RC100; completes, at the contacts 181, a holding circuit, including the grounded hold conductor 080| for energizing the winding thereof; and interrupts, at the contacts 188, the original operating circuit therefor. Upon operating the control relay R110 interrupts, at the contacts 11| and 113, the previously traced connections between the negative and positive line conductors of the trunk line |5 and the windings W106 and W184 of the repeating coil RC100; completes, at the contacts 112, a path for short-circuiting the winding W103 of the repeating coil RC166; and completes, at the contacts 114, a path for short-circuiting the left-hand winding of the answer relay R610.

Upon operating the start timer relay R650 completes, at the contacts 655, a circuit, including the contacts 66|, for operating the timer relay R645. Upon operating the timer relay R645 completes, at the contacts 648, a circuit for energizing the winding of the timer relay R665 in order to cause the latter relay to operate shortly thereafter, it being of the slow-to-operate type. Also the timer relay R645 completes, at the contacts 641, a holding circuit,` including the contacts 653, for energizing the lower winding of the start timer relay R650. When the timer relay R665 operates, it completes, at the contacts 666, a circuit for energizing the Winding of the timer relay R660; whereby the latter relay operates shortly thereafter, it being of the combination L slow-to-operate and slow-to-release type. Also the timer relay R665 completes, at the contacts 666, a multiple circuit including the contacts 863 for energizing the lower winding of the sequence relay R860; whereby the latter relay operates through its rst step to complete, at the contacts 862, a substantially identical path, including the grounded hold conductor C80| for short-circuiting the upper winding thereof, thereby positively to prevent operation of the sequence relay R860 through its sec-ond step at this time. When the timer relay R660 operates, it completes, at the contacts 662, a circuit for operating the control relay R640 and a multiple circuit, also including the contacts 654, for operating the rotary magnet M613 of the -timer switch TS610. When the rotary magnet M613 of the timer switch TS610 is thus operated, the wipers 61| and 612 thereof are driven away from their normal rotary positions one step in the rotary direction; whereby the set of switch springs S615 is closed in order to prepare a circuit traced hereinafter for operating the release magnet M614 of the timer switch TS610. Further the timer relay R660 interrupts,

at the contacts 66|, the circuit for energizing the winding of the timer relay R645 in order to cause the latter relay to restore shortly thereafter, it being of the slow-to-release type. Upon restoring the timer relay R645 interrupts, at the contacts 6418, the circuit for maintaining operated the timer relay R665. Upon operating the control relay R640 completes, at the contacts 642, a circuit for operating the control relay R630. Upon restoring the timer relay R665 interrupts, at the contacts 666, the circuit for energizing the winding of the timer relay R660 in order to cause the latter relay to restore shortly thereafter, it being of the combination slow-to-operate and slow-to-releas-e type. Also the timer relay R665 interrupts, at the contacts 666, the previously mentioned path for short-circuiting the upper winding of the sequence relay R860, whereby a circuit is completed, including the grounded hold conductor C| and the contacts 862, for energizing in series the upper and lower windings of the sequence relay R660 in order to cause the latter relay to operate through its second step.

At the conclusion of the seizure signal, the signal-in relay in the tone unit 60| restores to interrupt the application of ground potential to the signal conductor C606; whereby the signal-in relay R160 restores shortly thereafter, it being of the slow-to-release type. Upon restoring the signal-in relay R160 completes, at the contacts 162, the connection between the winding of the dial-in relay R1|0 and t-he dial conductor C6|0 extending to the tone unit 66|; and interrupts, at the contacts 163, the circuit Ifor energizing the upper winding of the start timer relay R650 in order to cause the latter relay to restore. Also the signal-in relay R160 interrupts, at the contacts 164, the circuit for energizing the winding of the control relay R in order to cause the latter relay to restore shortly thereafter, it being of the sloW-to-release type; and completes, at the contacts 166, a path, including the contacts 826, 846, 811 and 14|', for applying groundl potential to the pulse out-in conductor CGH. The application of ground potential to the pulse cut-in conductor C6|| brings -about operation of the pulse cut-in relay in the tone unit 60| in order to condition the impulse-in relay therein for operation as explained more fully hereinafter. Upon restoring the timer start relay R650 interrupts, at the contacts 654, the circuit for operating the rotary magnet M613 of the timer switch TS610. When the sequence relay R860 operates through its second step, it completes, at the contacts 86|, -a path for applying ground potential through the lower winding of the tandem test relay R840 to the EC conductor C8|4 of the trunk 8|0, which operation has no function in the present example since the call is being routed through the repeater 600 over the trunk 8|5 to the incoming selector 1805. Further, the sequence relay R860 completes, at the contacts 866, a connection, including the contacts 363 and 836 between the timer conductor C895 and the junction between the upper and lower windings of the time pulse relay R830. At this point, it is noted that ground potential is applied to the timer conductors C864 and C895 intermittently, ground potential being retained upon the timer conductor C894 when applied thereto throughout a time interval of approximately one minute and ground potential being retained upon the timer conductor C895 when applied thereto throughout a time interval of approximately ve minutes; which arrangement is utilized in conjunction with the time impulse relay R830A for a purpose more fully' explained hereinafter. When the timer relay R660 restores, it interrupts, at the contacts 662, the circuit for energizing the winding of the control relay R640 in order to cause the latter relay to restore shortly thereafter, it being of the slowto-release type. At this time the repeater 600 has been seized over the trunk line |5 by the repeater 300 and has, in turn, seized the incoming selector 805 over the trunk 8 I 5.-

'I'he'subscriber at the calling subscriber substation T2 having dialed the prefix digit previously mentioned, proceeds to dial the three digits comprising the directory number of the called subscriber substation TI. Specifically, the line relay R390 in the repeater 300 follows the impulses of the second digit dialed at the calling subscriber substation T2 and transmitted over the trunk 3 I 0. The rst time the line relay R390 restores, it interrupts, at the contacts 392, the holding circuit for maintaining operated the start pulse relay R420; and interrupts, at the contacts 39|, the path for applying ground potential to the receiving switch conductor C501 extending to the tone unit 50|. Upon restoring the start pulse relayvR42l completes, at the contacts 424, a circuit, including the contacts 404 and 494, for operating the pulse relay R525; completes, at the contacts 42|, a circuit, including the contacts 352, 381 and 465, for operating the contr-ol relay R410; and completes, at the contacts 42|, a multiple circuit, including the contacts 352 and 388, for energizing the upper winding of the prepare relay R495 in order to cause the latter relay to operate. Also the start pulse relay R420 interrupts, at the contacts 422, the circuit for energizing the Winding of the hold relay R400; however, the latter relay does not immediately restore as it is of the slow-to-release type. Upon operating the prepare relay R495 completes, at the contacts 491, a direct connection :between the sending -conductor C50| and the negative line conductor of'the trunk 515; and interrupts, at the contacts 495', a further point in the path for applying ground potential to the receiving switch conductor C501 extending to the. tone unit 50 I. Upon operating the control relay R410 interrupts, at the contacts 41| and 413, the connections between the monitoring conductor C503 and the monitoring |-oonduc tor C504 and the windings W403 and W404 of the repeating coil RC400; completes, at the contacts 412, the path for sh-ort-circuiting the winding W403 of the repeating coil RC400; completes, at the contacts 414, the path for short-#circuiting the right-hand winding of the answer relay R310; and completes, at the contacts 415 the holding circuit for energizing the lower winding of the prepare relay R495. Upon operating the pulse relay R525 completes, at the contacts 526, the circuit for operating the impulse relay R535; and completes, at 521, the oircuitfor energizing the upper winding of the pulse relay R520 in order to cause the latter relay to operate. Upon operating the impulse relay R535 interrupts, at the contacts 530, the path for shorting together the sending conductor 050| and the sending l-conductor C502; whereby the sending conductor C50| and the sending |conductor C502 are eiectively connected to the negative and Vpositive line conductors of the trunk line 515 as previously explained. Upon operating the pulse relay R520 completes, at the contacts 522, the circuit including the contacts424 and 404, vfor operating the pulse relay R490; and completes, at the contacts 52 I, a multiple holding circuit for lenergizing the winding of the impulse relay R535; Upon operating the pulse relay R490 completes, at the contacts 49|, the priming circuit, including the contacts 404' and the resistor 4|1, for energizing the winding of the start pulse relay R420; completes, at the contacts 493, a holding 18 circuit, including the contacts 4124 and 404, for energizing the windingsv thereof; and interrupts, at the contacts 494, the circuitfor maintainingv operated the pulse relay R525. Upon restoring the pulse relay R525 interrupts, at the contacts. 521, the` circuit for energizing the upper winding of the pulse relay R520 in order to cause the latterv relay to restore shortly thereafter, it being rendered slightly slow-to-release by virtue of the completed path, including the adjustable resistor 523 for short-circuiting the lower winding thereof.' Also the pulse relay R525 interrupts, at the contacts 52 B, the initial operating circuit for the impulse relay R535. Upon restoring the pulse relay R520 interrupts, at the contacts 52|, the circuit for maintaining 'operated'the impulse relay R535. Upon Vrestoring the impulse relay R535 completes, at. the contacts 536, the path for snorting together the sending conductor C501 and the sending -i-conductor C502, thereby effectively to disconnect 'the sending -conductor C50| andthe sending -i-conductor C502 from the negative and positive line conductors of the trunk line 5|5.

When the line relay R390 reoperates at the conclusion of the rst impulse of the second digit, it recompletes, at the contacts 39|, the circuit, including the contacts 405 and 402 for energizing thewinding of the hold relay R400; fand recompletes, at the contacts 392, a'circuit, including the contacts 494 and 528, for reoperating the start pulse relay R420. Upon reoperating the start pulse relay R420 interrupts, at the contacts 424, the holding circuit for retaining operated the pulse relay R490; and completes, at the `contacts 425, the holding circuit, including the re' sistor 4|5 and the contacts 392, for energizing Ithe winding thereof. Also the start pulse relay R420 interrupts, at theY contacts 42|, the circuit for energizing the winding of the control relay R410 in order to cause the latter relay to restore shortly thereafter, it being of the slow-to-release type. Further, the start pulse relay R420'com'- pletes, at the contacts 422, the circuit for energizing the winding of the hold relay R400. Upon restoring the .pulse relay R490 recompletes, at the contacts 492, the priming circuit, including the contacts 404, the resistor 4|9 and the adjust-'- able resistor 4|8, for energizing the winding thereof.

When the line relay R390`restores on the second pulse of the first digit, it again interrupts, at the contacts 392, the circuit for retaining operated the start pulse relay R420; whereby the pulse relay R525, the pulse relay R520, the pulse relay R490 and the impulse'relay R535 operate and'then restore in accordance with the cycle previously explained. Y In a similar manner, the. third and remainder of the impulses of the secondrdigit are repeated bythe line relay R390 to the impulse relay R535; whereby the impulse relay R535 opens, at the contacts 535, the path for snorting together the sending conductor C50| and the sending -i-conductor C502 ay plurality of times corresponding to the impulses of the second digit; i. e. theimpulse'relay R535'repeats the impulses of the second digit over the negative and positive line conductors of the trunk line 5|5. Since the hold relay R400 and the control relay-R410. are of the slow-to-release type, they remain-operated during the impulsing of the second digit; and at the conclusion of the second digit, the line relay R390v is retained 'in its operated position retaining, operated the start pulse 'relay R420. The operated start pulse relay R420 retains interrupted, at the contacts 42|,

, Y Y 19 the circuit for energizing the winding of' the control relay R410; whereby the latter relay restores shortly following the second digit.

Considering now the operation of the tone unit 50| at this time, the prepare relay R495 is retained in its operated position during the second digit by the operated control relay R410; whereby the operated prepare relay R495 retains interrupted, at the contacts 496', the path for applying ground potential to the receiving switch conductor C501. Also battery potential is applied via thecontacts 489, 369, 351 and the resistor 358 to the modulation cut-ofi conductor C508 during the second digit. The absence oi ground potential upon the receiving switch conductor C501V causes the receiving switch relay in the tone unit 50| to restore; whereby the tone unit 50| is converted from the receiving condition to the sending condition. The application of battery potential upon the modulation cut-off conductor C508 retains operated the modulation cut-off relay in the tone unit 50|; whereby the tone unit 50| is operative to send unmodulated 1000 cycle current over the sending conductor C50| and the sending -l-conductor C502. Accordingly, splashes of unmodulated 1000 cycle current appearing upon the sending ,-conductor 050| and the sending +conductor C502 are sent over the negative line conductor and the positive line conductor of the trunk line |5 as the contacts 536 are opened repeatedly by the impulse relay R535 following the line relay R390. Accordingly, the impulse relay R535 repeats the impulses received from the line relay rR390 in the form of splashes of unmodulated 1000 cycle current over the line conductors of the trunk line 5|5, and constituting a digit signal.

Shortly following the second digit, the control relay R410 restores as previously noted, recompleting, at the contacts 41| and 413, the conneci tion between the monitoring conductor C503 and the monitoring |conductor C502 and the windings W403 and W404 of the repeating coil RC400. Also the control relay R410 interrupts, at the contacts 412, the path for short-circuiting the winding W403 of the repeating coil RC400; interrupts, at the contacts 414, the path for shortcircuiting the right-hand winding of the answer relay R310; and interrupts, at the contacts 415, the holding circuit for energizing the lower winding of the prepare relay R495 in order to cause the latter relay to restore. Upon restoring the prepare relay R495 interrupts, at the contacts 495', the multiple holding circuit for energizing the Winding of the hold relay R400; recompletes, at the contacts 499, the priming circuit for energizing the upper winding of the pulse relay R520 and reconnects, at the contacts 496', ground potential to the receiving switch conductor C501. When ground potential is reapplied to the receiving switch conductor C501, the receiving switch relay in the tone unit 50| reoperates; whereby the tone unit 50| is converted from its sending position to its receiving position.

The digit signal corresponding to the second digit is transmitted over the line conductors of the trunk line 5|5 and received via the receiving conductor C805 and the receiving -l-conductor C006 by the tone unit 60|; whereby the tone unit 60|v responds thereto bringing about operation and restoration of the impulse-in relay therein. Specically, the impulse-in relay in the tone unit 60| follows the digit signal connecting and then disconnecting ground potential to the dial conductor C6|0 that is connected via the contacts 162 through the windingof the dial-in relay R1I0 to battery potential; whereby the dial-in relay R1| 0 follows the impulses of the second digit.` Each time the dial-in relay R1I0 operates and then restores, it completes and then interrupts,

at the contacts 1|2, a circuit, including the contacts 165, for operating the control relay R110; whereby the latter relay operates and remains operated during impulsing as it is of the sl0w-to release type. Also the rst time the dial-in relay R1|0 operates, it completes, at the contacts 1|2, a circuit, including the contacts 886, for energizing the upper winding of the conrtol relay R825 in order to cause the latter relay to operate. Upon operating the control relay R825 completes, at the contacts 826, a holding circuit, including the contacts 142', for energizing the lower winding thereof; and completes, at the contacts 321, a circuit, including the contacts 166 and the set of switch springs S615, for operating the release magnet M614 of the timer switch T5610. Upon operating the release magnet M614 releases the wipers 61| and 812 of the timer switch TS 610 and causes them to be returned to their normal rotary positions; whereby the set of switch springs S615 is opened to interrupt the circuit for operating the release magnet M514. Upon operating the control relay R110 interrupts, at the contacts 11| and 113, the connection between the negative and positive line conductors of the trunk line 5|5 and the windings W103 and W104 of the repeating coil RC; and completes, at the contacts 112, a path for short-circuiting the winding W103 of the repeating coil RC100. Also the control relay R completes, at the contacts 114, a path for short-circuiting the left-hand winding of the answer relay R810. Finally, each time the dial-in relay R1I0 operates and then restores, it interrupts and then recompletes, at the contacts 1| a point in the previously traced loop circuit extending via the line conductors C8|6 and C851 of the trunk 8|5 to the incoming selector 805; the contacts 1|! being bridged when open by the resistor 1|3 and the condenser 1|4 in order to prevent sparking thereof. Accordingly, the tone unit 60| receives the digit signal corresponding to the second digit and repeates the impulses thereof to the dial-in relay R1|0; whereby the latter relay repeats the impulses of the second digit, at the contacts 1| over the trunk 8|5 to the incoming selector 805. The selector 805 responds to the second digit selecting i-lrst the group of trunks, including the trunk 806, and then an idle trunk therein. For example, the incoming selector 805 may select the patricular trunk 806 extending to the combination connector 804; whereby the combination connector 804 is conditioned to respond to two digits transmitted over the trunk 806.

At the conclusion of the second digit, the impulse-in relay in the tone unit 60| restores removing ground potential from the dial-in conductor C6|0 in order to effect the restoration of the dial-in relay R1I0. Upon restoring the dial-in relay R1|0 recompletes, at the contacts 1| I, the loop circuit extending via the trunk 8|5, the incoming selector 805 and the trunk 805 to the combination connector 804; and interrupts, at the contacts 1|2, the circuit for energizing the winding of the control relay R110, whereby the latter relay restores shortly thereafter as it is of the slow-to-release type. Upon restoring the control relay R110 interrupts, at the contacts 112, the path for short-circuiting the winding W103 0f the repeating coil RC100; and recompletes, at. the contacts 11| and 113, theconnection-between the negative and positive line conductors of the trunk .line |5 and the windings W183 and W104 of the repeating coil RC18'8. Further the control relay R118 interrupts, at the contacts 114, the path for short-circuiting the left-hand winding of the answer relay R818.; whereby the latter winding is again insertedinto the loop circuit extending via the trunk 815 `to the combination connector 804.

In a similar manner, the third and fourth digits dialed at the calling subscriber `substation T2 are received over the trunk 3|8 Yby the repeater 380 and repeated over the trunk line 5| 5 to the tone unit 60| connected to the re- .peater 680; whereby the repeater 600 is controlled to repeat the third and. fourth digits over the trunk 815 to the combinationv connector 804; whereby the combination connector 804 is operated in accordance therewith to select the `subscriber line 80| extending to the called subscriber substation T-i. The subsequent operation of the combination connector 884 vdepends upon the'idle or-busy condition of the called'subscri'ber substation TI at this time.

First assuming that the called subscriber substation T| is idle at this time, the combination connector884 operates'to project ringing current o ver; the subscriber line 88| extending thereto in order-to operate the ringer thereat, indicatingF to thesubscriber at the called subscriber substation T-l that a call is waiting to be answered. Also the 4combination connector 804 operates to return ring-back tone current over the trunk 886, the incoming selector 885, the line conductors C816 and' C8|1 of the trunk 815 and the windings W18| and W102 of the repeating coil RC100`; whereby a corresponding ring-back tone current is induced in the windings W183 and` W10'4 of the repeating coil RC180 and traverses the connection including the contacts 11|, 113 andv 182, 184 and 196, and the line conductors of the trunk line 5|5'and thence via the receiving -conductor C585 andthe receiving -1-'conductor C586 into the tone unit 50|. The ring-back'tone current received over the receiving conductor C585 and the-receiving -l-conductor C506 by the tone unit 58| is amplied therein and impressed upon the Lmonitoring conductor C583 andthe monitoring -l-conductor C504; whereby it traversesv the connection, including the Vcontacts 48|, 483v and 41|, '4.13 and the windings W48`3 and W484of the repeating coil RC4881; whereby a corresponding ring-back tone current is induced in the windings W48! and W482 of the. repeating coil RC400 Aand returned over the line conductors C3|| and C312 of the trunk 5|8 and consequently. the selector 233., the finder 232 and the subscriber line 23| to the calling subscriber substation T2. Accordingly, the ring-back tone current returned from the combination connector 884 in the distant exchange 30 is received by the tone unit 50| in thecentral oiiice 28 and amplied and returned over the loop extending to the calling subscriber substation T2 in the central oiiice 28.

When the subscriber at the called'subscriber substation TlA answers the call, the combination connector 884 operates to reverse the polarity over the loop circuit extending back to the lefthand winding of the answer relay R818; whereby the latter relay is poled to operate; and to interrupt the return of ring-back tone current over the connection. Upon operating the Vanswer relay R810 completes, at the contacts 81|, a circuit, including the contacts 63| 185vand 16|,

andthe grounded hold conductor C|, for operatingthe reverse battery relay R; and completes, at the contacts 81|, a multiple circuit, including the contacts 64|, 88| and 815, for energizing the upper winding of the answer supervisory relay R815 in order to cause the latter relay to operate; and completes, at the contacts 812, a circuit, including the contacts 819, 161 and 66|, for operating the timer relay R645. Upon operating the reverse battery relay R130 interrupts, atvthe contactsf136, a further point in a holding circuit traced hereinafter for energizing in series the upper and lower windings of the time pulse relay R830; and interrupts, at the contacts 13|., the normal connection between the sending conductor C68| extending to the tone unit 60| and the receiving conductor C685 extending to the tone unit 68| and consequently the negative line conductor ofthe trunk line 5|5. The answer supervisory relay R815 operates only through its'rst step to complete, at the contacts 816, a path substantially identical to that previouslytraced for short-circuiting the lower winding thereof in order positively to prevent the latter relay from operating through its second step at thisvtime. Upon operating the timer relay R645 completes, at the contacts 648, a circuit for energizing the winding of the timer relay R665, thereby to cause the latter relay to operate shortly thereafter, it being of the slow-tooperate type. Also the timer relay R645 completes, at the contactsV 649, a holding circuit, including'the contacts 161 and 66|, for energizing the winding thereof; and completes, at the contacts 641, a circuit, including the contacts 652, for energizing the upper winding of the preparel relay R in order to cause the latter. relay to operate. Further, the timer relay R645 completes, at the contacts 641 andv 646, a multiple circuit, including the contacts 652, forenergizing the upper winding of the pulse relay R620 in order to cause the latter relay to operate. When thel pulse relay R628 operates, it completes, at the contacts 62|. a circuit for operating the impulse relay R635. Upon operating the impulse relay R635 interrupts. at the contacts 636, the normal path for shorting together the sending conductor C601 and the sending -i-conductor C682, Upon operating the prepare relay R195 interrupts, at the contacts 196, the connection between the negative line conductor of the trunk line 5|5 and the winding W183 of the repeatingr coil RC100; and completes, at the contacts 191, a connection between the sending conductor C681 and the negative linel conductor of the trunk line 5|5. Also at this time, the sending -l-conductor C602 is connected by way of the condenser 631 and the resistor 638 to thev positive line conductor of the trunk line 5| 5.' Further, the preparerelay R195 interrupts, at the contacts 196', the path for applying ground potential to the receiving switch conductor C681 eX- tending to the tone unit 60|. When ground potential is-thus removed from the receiving switch conductor C601, the receiving switch relay in. the tone unit 68| restores converting the tone unit 88| from its receiving position to its sending position; whereby the tone unit 68| operates at thisY time, to transmit 60 cycle modulated 1000 cycle current over the sending -conductor C60| andthe sending -l-conductor C682 which are connected a-t this time to the negative and the positive line conductors of the trunk line 5|5.

When the timer relay R665 operates it completes; atthecmtaCts 666, a circuit for energiz- 

